Walk certain streets in Manhattan in the sweltering summer, and you could pass a gauntlet of cool air… flowing out wide-open storefronts. I mean purposely propped open, not just open from customers passing through doorways.

It’s a not-too-subtle psychological trick to entice customers to step in out of the heat. So is this a business right, another opportunity for owners to get an extra competitive edge, or is it an environmental affront that affects us all?

This week New York City’s Mayor Michael Bloomberg signed a first-of-its-kind law that takes aim at the practice in the name of energy conservation. The Natural Resources Defense Council (NRDC), which helped the city prepare the legislation, hopes the law will serve as a model for other cities, helping the fight against global warming and air pollution, and relieving pressure on over-stressed power grids.

(Article continues below)

An NRDC analysis had found that a business with a typical 6 foot by 7 foot doorway in the Big Apple wastes up to $1,000 dollars and about a ton of CO2 in a summer if it leaves itâ€™s door open with the a/c on. Put another way, the Long Island Power Authority has estimated that stores who do the wasteful practice burn through 20-25% of the air-conditioning use.

According to the New York Times’s CityRoom blog, electronics stores are known to be the biggest offenders, though the practice is common along Fifth Avenue and 34th Street. The law was written to target stores with 4,000 square feet, or small stores that are part of a chain with five or more stores in New York City. The Department of Consumer Affairs would issue a warning to first-time offenders, while repeat violations would be fined $200, then $400.